Grain boundary segregation of copper, tin and antimony in C-Mn steels at 900°C

Abstract

The segregation of copper, tin and antimony to austenite grain boundaries at 900° C has been investigated in C-Mn steels using a scanning Auger microprobe (SAM). The specimens for microanalysis were prepared in a manner such that the prior austenite grain boundaries could be exposed by fracturing at room temperature in the UHV chamber of the SAM unit. Initial bulk concentrations ranged between 600 and 2600 ppm Cu, 50 and 360 ppm Sn and 8 and 35 ppm Sb. Significant enrichment of copper, tin and antimony was detected along the austenite grain boundaries. The grain boundary concentration of copper and tin was found to vary depending upon the initial bulk concentration while the average concentration of antimony at the grain boundaries was found to be approximately 1 at % for all of the heats studied. For heats in which a significant level of copper segregation was detected, a relationship of at % Cu = at % (Sn+Sb) at the austenite grain boundaries was observed. Deformation at 900° C prior to fracture in UHV was found to be necessary to promote segregation. Samples that were annealed at 900° C but not hot worked did not exhibit evidence of copper, tin or antimony segregation. These results have been interpreted in terms of the effects of deformation on segregation kinetics, and were correlated with hot ductility measurements made at 900° C.